On Sep 21, 1:32*am, Ian White GM3SEK wrote:
christofire wrote:

"Roy Lewallen" wrote in message
...
Antonio Vernucci wrote:
. . .
Under the assumption that dielectric loss is negligible, a permittivity
2.26 time higher than that of air results in a lower inner conductor
diameter, for a given outer diameter cable and a given impedance. *.. .

Yes, and this is why foamed dielectric cable has lower loss than solid
dielectric cable. Not because of lower dielectric loss (at least below a
few GHz), but because it has a larger center conductor for the same
impedance and outside diameter.

Roy Lewallen, W7EL

You've got it ... spread the word to all those amateurs who are hung up on
(negligible) dielectric loss!

It isn't the amateurs so much as the advertising. Marketing departments
highlight the foam dielectric because it's more obvious, and pretty soon
even the manufacturers are believing their own publicity.

As for the 50-ohm impedance, the reasons why it became an industry
standard are interesting but purely historical. The reason for using it
now is almost exclusively because it *is* an industry standard.

--

73 from Ian GM3SEK * * * * 'In Practice' columnist for RadCom (RSGB)http://www.ifwtech.co.uk/g3sek

Resonance means little. It is like reverse engineering where it is
assumed or understood that the transmission line will be 50 ohms! The
point to remember is that the less the resistive component that one
measures at the antenna the more the power is shifting over from the
resistive loss to the radiative resistance and nothing more. For
matching there is an advantage when the load is totally resistive
because the matching becomes less complicated. Obviously as more
energy is shifted over to radiative purposes it is more difficult to
feed as we do not know how to switch power transmission from a
parallel line to a singular line. But the fact remains, the less the
resistive losses the more power goes to radiation which is exactly
what you are trying to achieve.